batman-adv: Fix conditional statements indentation

commit 29b9256e6631 ("batman-adv: consider outgoing interface in OGM
sending") incorrectly indented the interface check code.
Signed-off-by: NSven Eckelmann <sven@narfation.org>
Signed-off-by: NMarek Lindner <mareklindner@neomailbox.ch>
Signed-off-by: NAntonio Quartulli <antonio@meshcoding.com>